Enhancing the Intermediate Vision of Monofocal Intraocular Lenses Using a Higher Order Aspheric Optic.

PURPOSE: To describe and evaluate a new monofocal intraocular lens (IOL) designed to improve intermediate vision using a unique refractive technology. METHODS: The new monofocal lens is based on a higher order aspheric optic and is designed to improve intermediate vision. Simulated visual acuity from far to -2.00 diopters (D) was calculated using optical bench data. The effect of corneal higher order aberrations (HOAs) on simulated visual acuity, pupil size, and decentration was assessed using realistic computer eye models. The susceptibility to photic phenomena was evaluated by measuring preclinically the intensity of the light distribution in the retinal plane. The new lens design was compared to a standard aspheric monofocal IOL that shares the same platform, material, and primary spherical aberration as the new design. RESULTS: Simulated defocus curves showed increased simulated visual acuity in the intermediate range compared to a standard aspheric monofocal IOL with comparable distance vision, independently of the pupil size and corneal HOAs. At -1.50 D, the new IOL design provided a gain of approximately 0.1 logMAR, whereas at distance, the difference was less than 0.05 logMAR. The tolerance to decentration was also similar in both designs. Finally, experimental results indicate that the susceptibility to photic phenomena with the new lens design was similar to that of a standard aspheric monofocal IOL. CONCLUSIONS: Preclinical data showed that the new lens design improves intermediate vision while maintaining comparable distance image quality and keeping the same photic phenomena profile as a standard aspheric monofocal IOL. [J Refract Surg. 2020;36(8):520-527.].

Effect of the equivalent refractive index on intraocular lens power prediction with ray tracing after myopic laser in situ keratomileusis.

PURPOSE: To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing. SETTING: AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. DESIGN: Retrospective data analysis. METHODS: The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery. RESULTS: The study evaluated 25 patients. The mean and range of ERI values determined using post-LASIK data were similar to those determined from pre-LASIK data. Introducing individual or an average ERI in the ray-tracing IOL power calculation procedure resulted in mean IOL power errors that were not significantly different from zero. The ray-tracing procedure that includes an average ERI gave a greater percentage of eyes with an IOL power prediction error within ±0.5 diopter than the Haigis-L (84% versus 52%). CONCLUSION: For IOL power determination in post-LASIK patients, custom ray tracing including a modified ERI was an accurate procedure that exceeded the current standards for normal eyes.

Explanted multifocal intraocular lenses.

UNLABELLED: We report 2 cases in which single-piece multifocal acrylic intraocular lenses (IOLs) were explanted because of complications related to the presence of glistenings in the bulk of the IOL optic. In both cases, the patients complained about blurry or hazy vision. In vivo slitlamp examinations prior to IOL explantation confirmed the presence of severe glistenings in the IOL optic in 1 case and moderate glistenings in the second case. In the first case, the symptoms resolved and both corrected and uncorrected distance visual acuities improved by 4 lines following IOL exchange with a monofocal IOL. In the second case, the visual symptoms persisted with a hard contact lens. Symptoms resolved following an exchange with a monofocal IOL that was free of glistenings. These findings indicate that straylight caused by IOLs with glistenings may be clinically significant in cases in which multifocal IOLs are implanted and patients require optimized retinal sensitivity. FINANCIAL DISCLOSURE: Mr. van der Mooren, Ms. Langeslag, and Dr. Piers are employees of Abbott Medical Optics, Inc. Drs. Steinert and Tyson are consultants to Abbott Medical Optics Inc.

Extending the range of vision using diffractive intraocular lens technology.

PURPOSE: To describe and to experimentally assess a new intraocular lens (IOL) design using new diffractive technology. SETTING: AMO Groningen b.v., Groningen, Netherlands. DESIGN: Experimental study. MATERIALS AND METHODS: The basic principles of the new diffractive technology are described. The new IOL comprises two diffractive technologies; one is designed to extend the range of vision by elongating the focus, and the other increases the retinal image contrast by correcting chromatic aberration. To assess the potential visual performance, simulations were carried out in clinically verified eye models to predict the clinical defocus curves (visual acuity). The optical performance of the new lens design was evaluated by optical measurements in a model eye. The model eye had a cornea having the spherical aberration and chromatic aberration of an average cataract patient. The measurements were performed in white light and monochromatic light. RESULTS: The simulations suggested an increase in visual acuity of 0.27 logMAR as compared to an aspherical monofocal IOL in the range from -1 to -3 diopter defocus. The white light modulation transfer function in the far focus was identical to that of a monofocal IOL. The new lens demonstrated negative chromatic aberration, therefore showing the capability to actively reduce ocular chromatic aberration. The experiments also show retinal image characteristics of an extended light source that suggest that dysphotopsias (halos) of the new IOL are comparable to those associated with monofocal IOLs. CONCLUSIONS: The application of new IOL diffractive technology enabled optical characteristics that suggested that an extended range of vision can be obtained without compromising distance vision. FINANCIAL DISCLOSURE: All authors are employees of Abbott Medical Optics, Inc.

Impact of intraocular lens material and design on light scatter: In vitro study.

PURPOSE: To determine the typical in vitro straylight levels for intraocular lenses (IOLs) of different materials and designs. SETTING: Abbott Medical Optics, Inc., Groningen, the Netherlands. DESIGN: Experimental study. METHODS: Two optical bench setups were used to determine baseline straylight levels of IOLs placed in a saline-filled cuvette: one for forward scatter positions between 0.6 and 3.0 degrees and one for positions up to 22.0 degrees. Line-spread functions were measured using the small-angle setup, and scattered light intensity was measured using the wide-angle setup. From these measurements, the angular dependent straylight parameter was calculated. Ten IOLs of different materials (hydrophobic and hydrophilic) and designs (monofocal or diffractive multifocal and spheric or aspheric) were studied, and their measured straylight levels were compared with the levels in a 20-year-old and a 70-year-old healthy noncataractous human crystalline lens. RESULTS: Irrespective of the material or design, monofocal IOLs had straylight levels below or close to those of a 20-year-old human crystalline lens. Diffractive multifocal IOLs had straylight levels higher than those of monofocal IOLs but less than those of a 70-year-old human crystalline lens. With increasing angle, hydrophobic IOLs showed a gradual decrease in straylight level. After an initial decrease, hydrophilic IOLs showed an increase in straylight level for larger angles. CONCLUSIONS: The baseline straylight levels of IOLs were design and material dependent (hydrophobic < hydrophilic; monofocal < diffractive multifocal). Most monofocal IOLs had straylight levels below the levels in a 20-year-old human crystalline lens.

Theoretical performance of intraocular lenses correcting both spherical and chromatic aberration.

PURPOSE: To assess the performance and optical limitations of intraocular lenses (IOLs) correcting both longitudinal spherical aberration (LSA) and longitudinal chromatic aberration (LCA) compared to standard spherical and aspheric IOLs. METHODS: Using a set of 46 white light, pseudophakic eye models representing a population of cataract patients, retinal image quality was assessed for three IOL designs-standard spherical IOLs; aspheric IOLs, correcting a fixed amount of LSA; and aspheric refractive/diffractive IOLs, correcting a fixed amount of LSA and LCA. Depth of field and tolerance to IOL misalignments were also assessed. RESULTS: The improvement factor, based on the area under the radial polychromatic modulation transfer function (pMTF) curve of the IOL, correcting both average LSA and LCA over the aspheric IOL was 1.19±0.12, and over the spherical IOL was 1.43±0.29. Within the range of ±1.00 diopter of defocus, pMTF of the IOL correcting both LSA and LCA was equal or higher than both the spherical and aspheric IOLs. The IOL could be decentered up to 0.6 to 0.8 mm before the performance degraded below that of a spherical IOL. CONCLUSIONS: This is the first study that evaluates IOLs correcting both LSA and LCA in the presence of corneal higher order aberrations. Intraocular lenses that correct both LSA and LCA improve simulated retinal image quality over spherical IOLs and IOLs that correct LSA alone, without sacrificing depth of field or tolerance to decentration. Correction of LCA in combination with LSA shows the potential to improve visual performance.

Spherical aberrations of human astigmatic corneas.

PURPOSE: To evaluate whether the average spherical aberration of human astigmatic corneas is statistically equivalent to human nonastigmatic corneas. METHODS: Spherical aberrations of 445 astigmatic corneas prior to laser vision correction were retrospectively investigated to determine Zernike coefficients for central corneal areas 6 mm in diameter using CTView (Sarver and Associates). Data were divided into groups according to cylinder power (0.01 to 0.25 diopters [D], 0.26 to 0.75 D, 0.76 to 1.06 D, 1.07 to 1.53 D, 1.54 to 2.00 D, and >2.00 D) and according to age by decade. Spherical aberrations were correlated with age and astigmatic power among groups and the entire population. Statistical analyses were conducted, and P<.05 was considered statistically significant. RESULTS: Mean patient age was 42.6±11 years. Astigmatic corneas had an average astigmatic power of 0.78±0.58 D and mean spherical aberration was 0.25±0.13 µm for the entire population and approximately the same (0.27 µm) for individual groups, ranging from 0.23 to 0.29 µm (P>.05 for all tested groups). CONCLUSIONS: Mean spherical aberration of astigmatic corneas was not correlated significantly with cylinder power or age (P>.05). Spherical aberrations are similar to those of nonastigmatic corneas, permitting the use of these additional data in the design of aspheric toric intra-ocular lenses.

Population-based visual acuity in the presence of defocus well predicted by classical theory.

According to classical theory, visual acuity (VA) can be modeled using the intersection of the eye's modulation transfer function with a retinal threshold function. To date, there have been limited attempts to validate this methodology by comparing theory with actual measured data. We use the methodology to predict the visual acuity in the presence of defocus of a population of cataract patients implanted with diffractive multifocal intraocular lenses. For the prediction, we used a set of physiological eye models that include chromatic and higher order aberrations. We found that the simulations correlated strongly to the clinical outcomes (R(2)=0.93). While the simulated VA of the eye models was systematically 0.05 logMAR units lower (better acuity) than the clinical results, this difference was independent of defocus (p=0.98). These results show that when the simple and straightforward classical theory is applied using physiological eye models, accurate predictions of the VA, and through-focus VA of a population can be made. This method may be suited for predicting visual performance of new cataract and refractive treatments.

Use of adaptive optics to determine the optimal ocular spherical aberration.

PURPOSE: To explore the impact of spherical aberration (SA) on contrast sensitivity using an adaptive optics vision simulator to determine the optimal amount of SA to include in customized corrections of wavefront aberrations. SETTING: Laboratorio de Optica, Universidad de Murcia, Murcia, Spain, and AMO Groningen BV, Groningen, The Netherlands. METHODS: An adaptive optics vision simulator consisting of a wavefront sensor, a 97-segmented deformable mirror to induce and correct aberrations of the eye, and a visual testing path was constructed for this study. The deformable mirror allows the effective ocular wavefront aberration to be manipulated and the resulting visual performance to be measured simultaneously. Subjective measurements of contrast sensitivity at 15 cycles per degree were performed with a 4.8 mm pupil in 5 subjects with different levels of naturally occurring SA. Contrast sensitivity was measured when SA values of -0.09 microm, 0.0 microm, 0.09 microm, and 0.182 microm were induced when the other natural aberrations of the eye were present, when the aberrations were corrected, and at defocus values of +/-0.25 diopter (D) and +/-0.50 D. RESULTS: Subjects experienced peak contrast sensitivity performance with varying levels of SA when their natural aberrations were present; however, average contrast performance peaked at 0 mum of SA. When all higher-order aberrations were corrected, all 5 subjects' peak performance occurred at 0 microm of SA. CONCLUSIONS: The adaptive optics vision simulator reduced the root-mean-square wavefront aberration of the eye by up to a factor of 4 and allowed noninvasive testing of the visual performance resulting from any ocular wavefront aberration introduced by customized correction procedures. This study showed that, on average, contrast performance peaked when SA was completely corrected.

Theoretical comparison of aberration-correcting customized and aspheric intraocular lenses.

PURPOSE: To assess the performance and optical limitations of standard, aspheric, and wavefront-customized intraocular lenses (IOLs) using clinically verified pseudophakic eye models. METHODS: White light pseudophakic eye models were constructed from physical measurements performed on 46 individual cataract patients and subsequently verified using the clinically measured contrast sensitivity function (CSF) and wavefront aberration of pseudophakic patients implanted with two different types of IOLs. These models are then used to design IOLs that correct the astigmatism and higher order aberrations of each individual eye model's cornea and to investigate how this correction would affect visual benefit, subjective tolerance to lens misalignment (tilt, decentration, and rotation), and depth of field. RESULTS: Physiological eye models and clinical outcomes show similar levels of higher order aberration and contrast improvement. Customized correction of ocular wavefront aberrations with an IOL results in contrast improvements on the order of 200% over the control and the Tecnis IOLs. The customized lenses can be, on average, decentered by as much as 0.8 mm, tilted > 10 degrees , and rotated as much as 15 degrees before their polychromatic modulation transfer function at 8 cycles/degree is less than that of the Tecnis or spherical control lens. Correction of wavefront aberration results in a narrower through focus curve but better out of focus performance for +/- 0.50 diopters. CONCLUSIONS: The use of realistic eye models that include higher order aberrations and chromatic aberrations are important when determining the impact of new IOL designs. Customized IOLs show the potential to improve visual performance.

Adaptive optics simulation of intraocular lenses with modified spherical aberration.

PURPOSE: Adaptive optics systems can be used to investigate the potential visual benefit associated with correcting ocular wave-front aberration. In this study, adaptive optics techniques were used to evaluate the potential advantages and disadvantages associated with intraocular lenses (IOLs) with modified spherical aberration profiles. METHODS: An adaptive optics vision simulator was constructed that allows psychophysical tests to be performed while viewing targets through any desired ocular wave-front profile. With this simulator, the subjective visual performance of four subjects was assessed by letter acuity and contrast sensitivity (at 3, 6, and 15 cyc/deg) for two different values of induced spherical aberration. The values of spherical aberration were chosen to reproduce two conditions: the average amount measured in pseudophakic patients with implanted IOLs having spherical surfaces and the complete correction of the individual's spherical aberration. Visual performance was assessed in both white and green light, at best focus and for defocus of +/-0.5 and +/-1.0 D. RESULTS: There was an average improvement in visual acuity associated with the correction of spherical aberration of 10% and 38% measured in white and green light, respectively. Similarly, average contrast sensitivity measurements improved 32% and 57% in white and green light. When spherical aberration was corrected, visual performance was as good as or better than for the normal spherical aberration case for defocus as large as +/-1 D. CONCLUSIONS: Correcting ocular spherical aberration improves spatial vision in the best-focus position without compromising the subjective tolerance to defocus.

Improved functional vision with a modified prolate intraocular lens.

PURPOSE: To evaluate whether the Tecnis Z9000 intraocular lens (IOL) (Pfizer) with a modified prolate anterior surface provides better quality of vision than a conventional spherical IOL. SETTING: Oregon Eye Institute, Eugene, Oregon, USA. METHODS: Patients presenting for cataract surgery who were randomly assigned to receive a Tecnis Z9000 IOL (Pfizer) or a Sensar OptiEdge AR40e IOL (AMO) in 1 eye were followed for 3 months postoperatively. The patient could elect to have the same type of IOL implanted in the fellow eye. The results of sine-wave grating contrast sensitivity testing under mesopic and photopic conditions were compared interindividually. RESULTS: Monocular comparison was made between the 2 IOL groups, which comprised 15 patients each. The Tecnis IOL provided significantly better contrast sensitivity at 6 cycles per degree (cpd) under photopic conditions and at 1.5 and 3 cpd under mesopic conditions. Seven patients with a Tecnis IOL and 9 patients with an AR40e IOL had subsequent implantation in the fellow eye. In all eyes, including fellow eyes, having IOL implantation, the Tecnis provided significantly better contrast sensitivity at 3 and 6 cpd under photopic conditions and at 1.5, 3, and 6 cpd under mesopic conditions. The mean contrast sensitivity in fellow eyes showed that the Tecnis IOL produced significantly better results at some spatial frequencies. CONCLUSIONS: Results show the Tecnis IOL with a modified prolate anterior surface may produce better contrast sensitivity than a standard spherical IOL under mesopic and photopic conditions. Because contrast sensitivity testing correlates well with functional vision, a goal of future research should be to evaluate patient performance using functional tests such as driving simulation.

Eye models for the prediction of contrast vision in patients with new intraocular lens designs.

Theoretical calculations of the polychromatic modulation transfer function (MTF) and wave-front aberration were performed with physiological eye models. These eye models have an amount of spherical aberration that is representative of a normal population of pseudophakic eyes implanted with two different types of intraocular lens (IOL) made from high-refractive-index silicone. These theoretical calculations were compared with the measured contrast sensitivity function (CSF) under mesopic lighting conditions and with wave-front aberration (obtained with a Hartmann-Shack wave-front sensor) collected from 37 patients bilaterally implanted with the same types of lens. The relationships between the ocular wave-front aberration and the MTF predicted by the eye models and the CSF and the ocular wave-front aberration measured in eyes implanted with IOLs were investigated. The predicted improvements in MTF and wave-front aberration correlated well with the improvements measured in practice. Physiological eye models are therefore useful tools for IOL design.

A new intraocular lens design to reduce spherical aberration of pseudophakic eyes.

PURPOSE: The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. METHODS: Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. RESULTS: Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL. This improvement occurred without an apparent loss in depth of focus. CONCLUSION: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients.

Prospective randomized trial of an anterior surface modified prolate intraocular lens.

PURPOSE: We compare the contrast sensitivity obtained with an anterior surface modified prolate intraocular lens with the contrast sensitivity obtained with a standard spherical intraocular lens. METHODS: Patients presenting for cataract surgery in one eye were randomized to receive either the Tecnis Z9000 intraocular lens (Pharmacia) or the AMO AR40e Opti-Edge intraocular lens (AMO). Sine wave grating contrast sensitivity testing under mesopic and photopic conditions served as the principal outcome measure. RESULTS: The Tecnis Z9000 intraocular lens provided statistically significantly better contrast sensitivity at 1.5 and 3 cycles per degree under mesopic conditions and at 6, 12 and 18 cycles per degree under photopic conditions. CONCLUSION: The use of a modified prolate intraocular lens during cataract surgery has the potential to improve contrast sensitivity under both mesopic and photopic conditions.